With the invention of the present applicants quick change bit holder as disclosed in U.S. Pat. No. 6,585,326, issued Jul. 1, 2003, the combination of bits and their respective bit holders whether separate pieces or combined into a unitary structure, no longer needed threaded nuts or retaining rings to maintain the structure on a bit block as part of a rotating drum or endless chain type of bit assembly mechanism. The respective shanks of the bit/holder combinations were generally cylindrical in shape, hollow with a thick generally annular side wall and slotted on a distal portion of that side wall in an axially inward direction allowing for radial compression when inserted in a bit block bore having sufficient radial force between that shank and bore to maintain the bit holder in the bit block during use.
In the preferred embodiment, the bit block bore would be tapered in a non-locking taper configuration approximating one degree of taper per side and the shank of the bit holder would likewise be tapered along a portion of its length such that the insertion of the bit holder shank in the bit block bore need only be forced approximately ½ to 1¼ inch to mount the bit holder shank in the bit block bore.
Differing configurations made by others utilizing applicant's basic invention were, secondly, configured with either near a perfectly cylindrical bit block bore and a cylindrical distal end of the slotted bit holder shank. Such a configuration required forcing the bit holder shank into the bit block bore a distance of about two inches to retain the assembly together during use.
A third configuration was developed utilizing a bit block bore that at approximately its outer ½ axial length included a frustoconical shape taper approximating 5.5 degrees per side with the inner portion of its axial length being cylindrical in shape. The distal end half of the bit holder shank was slotted in a configuration useful with the third type of bit block bore. The present applicant's prior application Ser. No. 12/870,289 disclosed a bit holder shank in FIG. 12 capable of being retained in the third type of bit block bore, namely, the inner half being cylindrical and the outer half being tapered with FIGS. 13 and 14 showing that same bit holder shank being inserted in a bit block having a slight (one degree per side) constant taper bore.
The invention shown in the previously mentioned FIG. 12 of the '289 application discloses an upper portion of the bit holder shank immediately adjacent the upper bit holder body rear annular flange which does not contact the upper portion of the bit holder shank of the tapered bit block bore, but does have the rear annular flange contacting the upper flat horizontal surface of the bit block.
Competitive bit holder/bit block combinations were constructed such that when the bit holder shank was mounted in the bit block bore, the rear annular flange of the bit holder body would be spatially related to the upper surface of the bit block.
A need has developed for a new and improved bit holder shank capable of operating in the multiple bit holder bore configurations.